An Oldham coupling is a device in which two reciprocating motions at right angles permit an orbiting motion between two members coacting with the Oldham coupling. Basically, the Oldham coupling reciprocates sinusoidally relative to a first member while a second member reciprocates cosinusoidally relative to the Oldham coupling in a direction perpendicular to the direction of movement of the Oldham coupling. In this manner the second member goes through a circular orbiting motion with no relative rotation. Assuming that the Oldham coupling is circular, which is a common shape but not required for proper function, the outside clearance required for its movement is of an oval or racetrack shape, specifically two semicircles joined by a straight section. The inside clearance required for its movement consists of two intersecting circular arcs, each of equal radius and less that 180.degree. in extent, and with the axis joining the two points of intersection being perpendicular to the axis of travel of the Oldham coupling. As noted, the Oldham coupling is located between two members so that any supporting structure between the two members must pass through the plane of movement of the Oldham coupling. In devices such as scroll compressors which are typically located in cylindrical shells, the clearance needed for travel of the Oldham coupling may dictate the need for a larger diameter shell than would otherwise be the case. Assuming a cylindrical shell, most of the available space for the inner or outer support structure is in a direction perpendicular to the direction of travel of the Oldham coupling. Given the fact that at least some of the supporting structure needs to be located outside of the space required for movement of the Oldham coupling, the minimum enclosing shell diameter will be determined by a combination of the size of the inner supporting structure, the radial width of the Oldham coupling, the space required for the coupling's motion, and the size of the outer supporting structure. Since the inner support structure is typically round due to manufacturing considerations, there is some space available outside the inner support structure in a direction perpendicular to the direction of travel of the coupling which is essentially unavailable and is thus wasted. Reducing the radial thickness of the curved portions of the ring or outer support structure provides only a limited opportunity to reduce the shell diameter before structural integrity considerations arise.